The senses of hearing the balance are made possible by sensory hair cells of the inner ear. This proposed research is an investigation of the embryonic development of these sensory hair cells. The inner ears of all vertebrates contain hair cells that transduce minute displacements resulting from sound or acceleration into changes in membrane potential. Hair cells contain highly specialized pre-synaptic components, including specific types of voltage-gated calcium channels. Voltage-gated calcium channels help shape the hair cell membrane potential and play an essential role in synaptic transmission from hair cells onto auditory nerve fibers. Relatively little is known about the acquisition of calcium channels during auditory development. The specific aims of the proposed research are: (1) to characterize the acquisition of calcium channel transcripts by auditory and vestibular hair cells during Xenopus development using molecular cloning and in situ hybridization. (2) to analyze the acquisition of calcium currents by Xenopus saccular hair cells during embryonic and larval development using patch clamp electrophysiology. By studying how hair cells acquire calcium channels, we will begin to address fundamental questions such as how a hair cell establishes functional synapses. The inner ear of the amphibian Xenopus laevis provides an unusually good preparation for the investigation of auditory development. Because developmental mechanisms and many aspects of hair cell physiology are apparently well conserved among vertebrates, this research is likely to apply to other vertebrates, including humans.